Project Summary Endothelial cells regulate arterial smooth muscle cell contractility, thereby modulating regional organ blood flow and systemic blood pressure. Dysfunctional endothelial cell control of contractility is a hallmark of several cardiovascular diseases, including hypertension, but pathological mechanisms involved are poorly understood. Membrane potential controls endothelial cell functions, but ion channels involved and functional significance are unclear. Several members of the transient receptor potential (TRP) family, are expressed in endothelial cells, but physiological functions are unclear. Similarly, several receptor ligands and stimuli are endothelium-dependent vasodilators, but their signaling mechanisms are poorly understood. Our preliminary data demonstrate that in endothelial cells, potassium (K+) channels are activated by nearby transient receptor potential (TRP) channels, leading to vasodilation. Data also suggest that K+ channel signaling is dysfunctional during hypertension. For this proposal, we will study K+ and TRP channel knockout mice. Three specific aims will be investigated. Aim 1 will test the hypothesis that K+ currents in endothelial cells regulate arterial hyperpolarization and vasodilation. Aim 2 will investigate the hypothesis that TRP channels stimulate K+ channels in endothelial cells, producing vasodilation. Aim 3 will study the hypothesis that systemic hypertension is associated with a pathological attenuation in K+ channel signaling in endothelial cells that inhibits vasodilation by these proteins. Methods used will include RT-PCR, Western blotting, biotinylation, FRET, RNAi, co-IP, immunofluorescence, patch-clamp electrophysiology, membrane potential recording, intracellular Ca2+ imaging, arterial myography and blood pressure telemetry. This proposal will provide significant novel information concerning vasoregulation by endothelial cell K+ channels.